They call them "legal highs" or, in the acronym driven drug lingo, NPS. Novel psychoactive substances are drugs that mimic the highs of banned substances like marijuana or cocaine, but their chemistry has been tinkered with just enough that they fall through the cracks of international drug control laws. Since about 2009 they've been flooding the market, with at times deadly results. Last month, New York, Mississippi and Alabama issued health alerts after a rash of overdoses, and police in Tuscaloosa, Alabama declared a public health crisis when one person died and two dozen were hospitalized after taking an NPS known on the street as "Spice." How can we stop the arms race in legal highs? Would legalization of marijuana and other recreational drugs end up safer for all?